1. Field of the Invention
This invention relates to catheterization of a patient and more particularly relates to a polyurethane catheter tubing of controlled pliability when it comes into contact with a body fluid.
2. Background of the Invention
Catheterization procedures conventionally include puncture of a patient's skin and insertion of a catheter into a body cavity, such as the blood stream, using some type of catheter insertion device. For patient comfort, it is highly desirable that the catheter be of the smallest possible cross-sectional area during insertion. It is nevertheless evident that the catheter lumen must be large enough to achieve the required rate of administration of a medicament solution or drainage of a body fluid through the catheter.
A number of polymeric materials have been investigated for fabrication of catheter tubing. Silicone rubber has been used, but this material, which is soft and pliable, requires inclusion of various additives such as fillers and plasticizers to give sufficient tensile strength. The thick wall needed to prevent collapse due to the pliability requires a large outside diameter to achieve sufficient inside diameter for fluid flow.
Other catheters of the prior art have been made of rigid substantially inflexible polymeric materials. Exemplary of such conventional catheters are the catheters of fluorinated ethylene propylene copolymer (FEP) having stripes of FEP containing a radiopaque agent disclosed by Coneys in U.S. Pat. No. 4,657,024.
Ostoich, in U.S. Pat. No. 4,211,741, disclose a catheter having a thin layer of polyurethane laminated on either or both surfaces of a thick polyvinyl chloride layer.
Recently, hydrophilic polymers which absorb water, often termed hydrogels, have been disclosed. U.S. Pat. No. 4,668,221 to Luther discloses a catheter made of hydrophilic polymer which fits over a stylet for insertion. This catheter, on contact with blood, swells and softens so that the stylet can be removed.
U.S. Pat. No. 4,883,699 to Aniuk et al. discloses a tubing having a nonhydrophilic polyurethane component and a hydrophilic polyvinyl alcohol component. The tubing is said to absorb water and swell while retaining tensile strength.
Polyurethanes which swell and soften in contact with a body fluid have been disclosed in recent years as an attractive material for catheters. Gould et al., in U.S. Pat. No. 4,454,309, discloses hydrophilic polyurethane diacrylate compositions which swell in water and may be molded and cured to form shaped products. U.S. Pat. Nos. 4,728,322 and 4,781,703 to Walker et al. disclose catheters fabricated of a composition which includes a nonhydrophilic first component and a hydrophilic polyurethane diacrylate second component. When contacted with a liquid, the composition swells and softens due to absorption of the liquid, causing the catheter to increase in cross-sectional area.
Polyurethanes as a class have several advantages as materials for catheters. In general, they have excellent blood compatibility. In addition, they absorb water, soften and thereby become more pliable. Pliability is a distinct aid in threading a catheter through a tortuous blood vessel to a desired placement.
While significant improvement in catheter performance has resulted from fabrication using polyurethane, there remains a need for a catheter having the blood compatibility, softness and pliability of polyurethane which retains sufficient mechanical strength and stiffness for ease of insertion and repositioning if desired. The present invention addresses this need.